Agricultural air seeders generally comprise a furrow opener arm pivotally attached to the frame. A furrow opener such as a disc, knife or hoe can be attached to a bottom end of the arm to engage the soil. The arm is maintained in a generally downward operating position by a bias element, and the mounting is such that the arm can move rearward and upward from the operating position, against the bias force, to clear obstacles or follow terrain.
Alternatively, on some air seeders an arm extends rearward and the operating position is dictated by a wheel attached to the rear end of the arm. The arm moves up and down against a downward force exerted by a bias element, following changes in terrain as the wheel moves up and down relative to the frame. Typically one or two further arms, or legs, extend downward from the arm and a furrow opener is attached to the bottom of each leg. In some air seeders as well, the bias element is a hydraulic cylinder operative to provide the necessary bias force, as well as to raise the furrow opener from the operating position. Such an air seeder is generally disclosed in U.S. Pat. No. 5,396,851 to the present inventor Beaujot.
In any event the furrow opener arm must move freely about its pivotal attachment to the frame. It is desirable to have the furrow opener held in a fixed lateral position to maintain seeding accuracy so the pivotal attachment must be substantially rigid laterally. While moving along a field in a straight line, the lateral forces on the arm are minimal, but during operations the arm is subjected to increased lateral forces when turning and/or when the furrow opener hits the edge of a rock, or like obstruction. The arm, generally made of steel, has some inherent resilience that allows it to flex sideways when subjected to high lateral forces, and then spring back to the properly aligned position.
These high lateral forces cause substantial stress on the pivot mechanism attaching the arm to the frame. The furrow opener is often a considerable distance from the pivot mechanism, such that considerable torque is applied, multiplying the lateral force exerted on the mechanism.
Typically, the pivot mechanism is provided by a bracket fixed to the frame with arm members on each side of the bracket, or alternatively a pair of brackets fixed to the frame, with the arm located between the brackets. A pivot pin through the bracket and the end of the arm provides the pivotal attachment of the arm to the frame. In addition to providing the required pivotal movement of the arm, the pin also exerts the forces required to resist the lateral forces exerted on the arm, and the pin is thus subjected to considerable lateral or bending forces.
Sometimes the brackets are quite widely separated, and the arm includes a lateral brace such that the arm and brace are attached by separate pins, one to each bracket. The wider spacing of the brackets provides at least some degree of torque on the arm to resist the lateral forces exerted on the arm.
A major problem with such conventional pivot mechanisms is that the lateral bending forces cause the pins and brackets wear. In normal operation the arm pivots about the pin, the pin experiences minimal bending forces, and wear is relatively even. Where lateral forces must be resisted, as in rocky fields or where sharp turns are frequent, the lateral force exerted by the pin on the bracket increases, increasing the friction force exerted between the pin and the bracket. This causes increased resistance to the required pivotal movement between the pin and brackets, and wear increases significantly.
In certain air seeders, such as the air seeder of the '851 patent to Beaujot, and that disclosed in U.S. Pat. No. 4,762,075 to Halford, the air seeder comprises two generally downward oriented legs attached to the pivoting arm, which is supported by a wheel. The legs are located one behind the other, and separated laterally. A furrow opener is attached to the bottom of each leg such that seed and fertilizer can be placed in separate furrows that that are laterally, and possibly also vertically, spaced so that the fertilizer does not damage the seed.
One of the difficulties this two leg type of seeder has to overcome is that of residue clearance. In no-till seeding, the residue from the previous year's crop is present on the surface of the field, and this residue must pass between the downward extending legs that carry the furrow openers. Where the residue is heavy, or where straws are long, the residue can be gathered by the furrow opener legs, and create a clump that is carried along, pushing soil and eventually plugging the seeder. Where there are two legs for each seed row, these residue clearance problems are multiplied.
The rear leg is commonly slightly offset to the side by 1 to 2 inches and is 8 to 15 inches behind the front leg. Where the furrow opener on the first leg is a knife or hoe type opener, the residue often builds up on this front opener from its raking action. This residue build-up tends to release in small or not so small clumps as the seeder travels through the previous year's residue. The bigger clumps of residue that build up on the front leg tend to ride up on the front leg due to the lifting and rolling effect of the soil movement at the bottom of the leg caused by the knife engaging the soil. As their mass and volume increase, or as they get nudged off balance, these clumps tend to roll off the front leg to one side or the other. When they roll off in the direction that the rear leg is offset, they tend to be caught by the rear leg and so must also clear this rear leg before passing out under the machine.